This invention relates generally to seal strips for a suction roll in a paper making machine in which the seal strips are uniquely constructed at least so far as an outer edge portion of the strip is concerned which engages an internal surface of a rotating perforated shell of the suction roll, the construction of the strips providing long wear characteristics by reducing friction and improving lubrication between the seal strips and the perforated shell.
In the art of paper making, various machines have been provided for forming paper webs from a pulp slurry with one such machine and method known in the art being the Fourdrinier machine. Such paper making machines include a suction roll underlying a screen belt or the like which includes a perforated cylindrical shell that is rotatably supported together with a stationary vacuum box disposed internally of the perforated shell and connected with a source of vacuum. The vacuum box includes a slotlike structure along one side thereof and seal strips along each side of the slot for engagement with the internal surface of the rotating shell in order to provide a sealing engagement between the vacuum box and the internal surface of the perforated shell so that the vacuum induced on the vacuum box is in communication with the internal surface of the perforated shell to remove water which may penetrate the shell. This structure is well known and typical of such structures is U.S. Pat. No. 2,578,551 issued Dec. 11, 1951. Many other examples of suction roll structures are illustrated in the prior patents classified in Class 162, subclass 371 and the patents in this subclass are incorporated herein by reference thereto. Typical of such structures is the provision of slots or grooves along the outer edges of the slotlike structure formed in the vacuum box with the slots or grooves receiving the seal strips for movement toward and away from the perforated shell. A tube is disposed between the inner edge of the seal strip and the bottom of the slot or groove which can be pneumatically or hydraulically expanded to move the seal strips into sealing engagement with the interior surface of the rotatable perforated shell. Due to the frictional contact between the seal strips and the shell, wear occurs on both the seal strips and shell with the seal strips having a reduced life expectancy and requiring replacement at periodic intervals. In view of the necessity to shut the paper making machine down while the seal strips are being replaced, the life expectancy of the seal strips is important. Also, it is important for the seal strips to maintain dimensional stability and have a reduced coefficient of friction with the perforated shell and not cause environmental pollution during normal use.